Add a COM STA Notice to base_shell_dialog_win.cc

Fallout from
https://chromium-review.googlesource.com/c/chromium/src/+/922662

BUG=

Change-Id: Ie77cfd226cc0af218068405190936348907c93cd
Reviewed-on: https://chromium-review.googlesource.com/952103Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541259}

ui/shell_dialogs/base_shell_dialog_win.cc

@@ -64,6 +64,7 @@ void BaseShellDialogImpl::DisableOwner(HWND owner) {
 // static
 base::Thread* BaseShellDialogImpl::CreateDialogThread() {
   base::Thread* thread = new base::Thread("Chrome_ShellDialogThread");
+  // Many shell dialogs require a COM Single-Threaded Apartment (STA) to run.
   thread->init_com_with_mta(false);
   bool started = thread->Start();
   DCHECK(started);